Fail if a generated file exists already

Closes #993

CHANGELOG.md

@@ -24,6 +24,10 @@ Model:
 
 - Change representation of null messages (#643)
 
+Generator:
+
+- Detect when a generated file would overwrite an existing file (#993)
+
 ### Removed
 
 Specification:

rflx/generator/generator.py

@@ -1465,10 +1465,8 @@ def _refinement_conditions(
 def create_file(filename: Path, content: str) -> None:
     log.info("Creating %s", filename)
 
-    try:
-        filename.unlink()
-    except FileNotFoundError:
-        pass
+    if filename.exists():
+        fail(f"file {filename} already exists", subsystem=Subsystem.GENERATOR)
     filename.write_text(content)
 
 

tests/unit/cli_test.py

@@ -118,14 +118,16 @@ def test_main_generate_no_library_files(tmp_path: Path) -> None:
 
 
 def test_main_generate_prefix(tmp_path: Path) -> None:
-    for prefix in ["", " ", "A", "A.B", "A.B.C"]:
+    for index, prefix in enumerate(["", " ", "A", "A.B", "A.B.C"]):
+        path = tmp_path / str(index)
+        path.mkdir()
         assert (
             cli.main(
                 [
                     "rflx",
                     "generate",
                     "-d",
-                    str(tmp_path),
+                    str(path),
                     "-p",
                     prefix,
                     MESSAGE_SPEC_FILE,

tests/unit/generator_test.py

@@ -143,6 +143,12 @@ def test_generate_missing_template_files(monkeypatch: MonkeyPatch, tmp_path: Pat
         Generator().generate(Model(), Integration(), tmp_path)
 
 
+def test_generate_existing_file(tmp_path: Path) -> None:
+    Generator().generate(models.TLV_MODEL, Integration(), tmp_path)
+    with pytest.raises(RecordFluxError, match="^generator: error: file [^ ]+ already exists$"):
+        Generator().generate(models.TLV_MODEL, Integration(), tmp_path)
+
+
 @pytest.mark.parametrize("model", MODELS)
 def test_equality(model: Model, tmp_path: Path) -> None:
     assert_equal_code(model, Integration(), GENERATED_DIR, tmp_path, accept_extra_files=True)